Unit I
Frame relay Networks
Frame Relay often is described as a streamlined version of X.25, offering fewer of the robust capabilities, such as windowing and retransmission of last data that are offered in X.25.
Frame Relay Devices
Devices attached to a Frame Relay WAN fall into the following two general categories:
• Data terminal equipment (DTE) • Data circuit-terminating equipment (DCE)
DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer. In fact, they may be owned by the customer. Examples of DTE devices are terminals, personal computers, routers, and bridges.
DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to provide clocking and switching services in a network, which are the devices that actually transmit data through the WAN. In most cases, these are packet switches. Figure 10-1 shows the relationship between the two categories of devices.
Standard Frame Relay Frame
Standard Frame Relay frames consist of the fields illustrated in Figure 10-4.
Figure Five Fields Comprise the Frame Relay Frame


Each frame relay PDU consists of the following fields:
1. Flag Field. The flag is used to perform high level data link synchronization which indicates the beginning and end of the frame with the unique pattern 01111110. To ensure that the 01111110 pattern does not appear somewhere inside the frame, bit stuffing and destuffing procedures are used.
2. Address Field. Each address field may occupy either octet 2 to 3, octet 2 to 4, or octet 2 to 5, depending on the range of the address in use. A two-octet address field comprising the EA=ADDRESS FIELD EXTENSION BITS and the C/R=COMMAND/RESPONSE BIT.
3. DLCI-Data Link Connection Identifier Bits. The DLCI serves to identify the virtual connection so that the receiving end knows which information connection a frame belongs to. Note that this DLCI has only local significance. A single physical channel can multiplex several different virtual connections.
4. FECN, BECN, DE bits. These bits report congestion:
o FECN=Forward Explicit Congestion Notification bit
o BECN=Backward Explicit Congestion Notification bit
o DE=Discard Eligibility bit
5. Information Field. A system parameter defines the maximum number of data bytes that a host can pack into a frame. Hosts may negotiate the actual maximum frame length at call set-up time. The standard specifies the maximum information field size (supportable by any network) as at least 262 octets. Since end-to-end protocols typically operate on the basis of larger information units, frame relay recommends that the network support the maximum value of at least 1600 octets in order to avoid the need for segmentation and reassembling by end-users.
Frame Check Sequence (FCS) Field. Since one cannot completely ignore the bit error-rate of the medium, each switching node needs to implement error detection to avoid wasting bandwidth due to the transmission of erred frames. The error detection mechanism used in frame relay uses the cyclic redundancy check (CRC) as its basis.
Congestion-Control Mechanisms
Frame Relay reduces network overhead by implementing simple congestion-notification mechanisms rather than explicit, per-virtual-circuit flow control. Frame Relay typically is implemented on reliable network media, so data integrity is not sacrificed because flow control can be left to higher-layer protocols. Frame Relay implements two congestion-notification mechanisms:
• Forward-explicit congestion notification (FECN)
• Backward-explicit congestion notification (BECN) FECN and BECN each is controlled by a single bit contained in the Frame Relay frame header. The Frame Relay frame header also contains a Discard Eligibility (DE) bit, which is used to identify less important traffic that can be dropped during periods of congestion.
Frame Relay versus X.25
The design of X.25 aimed to provide error-free delivery over links with high error-rates. Frame relay takes advantage of the new links with lower error-rates, enabling it to eliminate many of the services provided by X.25. The elimination of functions and fields, combined with digital links, enables frame relay to operate at speeds 20 times greater than X.25.
X.25 specifies processing at layers 1, 2 and 3 of the OSI model, while frame relay operates at layers 1 and 2 only. This means that frame relay has significantly less processing to do at each node, which improves throughput by an order of magnitude.
X.25 prepares and sends packets, while frame relay prepares and sends frames. X.25 packets contain several fields used for error and flow control, none of which frame relay needs. The frames in frame relay contain an expanded address field that enables frame relay nodes to direct frames to their destinations with minimal processing .
X.25 has a fixed bandwidth available. It uses or wastes portions of its bandwidth as the load dictates. Frame relay can dynamically allocate bandwidth during call setup negotiation at both the physical and logical channel level.
Asynchronous Transfer Mode (ATM)
Asynchronous Transfer Mode (ATM) is an International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells. ATM networks are connection-oriented.
ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic). It provides scalable bandwidth from a few megabits per second (Mbps) to many gigabits per second (Gbps). Because of its asynchronous nature, ATM is more efficient than synchronous technologies, such as time-division multiplexing (TDM).
With TDM, each user is assigned to a time slot, and no other station can send in that time slot. If a station has much data to send, it can send only when its time slot comes up, even if all other time slots are empty. However, if a station has nothing to transmit when its time slot comes up, the time slot is sent empty and is wasted. Because ATM is asynchronous, time slots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell.
ATM transfers information in fixed-size units called cells. Each cell consists of 53 octets, or bytes. The first 5 bytes contain cell-header information, and the remaining 48 contain the payload (user information). Small, fixed-length cells are well suited to transferring voice and video traffic because such traffic is intolerant of delays that result from having to wait for a large data packet to download, among other things. Figure illustrates the basic format of an ATM cell. Figure :An ATM Cell Consists of a Header and Payload Data


ATM Protocol architecture:

ATM is almost similar to cell relay and packets witching using X.25and framerelay.like packet switching and frame relay,ATM involves the transfer of data in discrete pieces.also,like packet switching and frame relay ,ATM allows multiple logical connections to multiplexed over a single physical interface. in the case of ATM,the information flow on each logical connection is organised into fixed-size packets, called cells. ATM is a streamlined protocol with minimal error and flow control capabilities :this reduces the overhead of processing ATM cells and reduces the number of overhead bits required with each cell, thus enabling ATM to operate at high data rates.the use of fixed-size cells simplifies the processing required at each ATM node,again supporting the use of ATM at high data rates. The ATM architecture uses a logical model to describe the functionality that it supports. ATM functionality corresponds to the physical layer and part of the data link layer of the OSI reference model. . the protocol referencce model shown makes reference to three separate planes:
user plane provides for user information transfer ,along with associated controls (e.g.,flow control ,error control).
control plane performs call control and connection control functions.
management plane includes plane management ,which performs management function related to a system as a whole and provides coordination between all the planes ,and layer management which performs management functions relating to resource and parameters residing in its protocol entities .
The ATM reference model is composed of the following ATM layers:
• Physical layer—Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission.
• ATM layer—Combined with the ATM adaptation layer, the ATM layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell.
• ATM adaptation layer (AAL)—Combined with the ATM layer, the AAL is roughly analogous to the data link layer of the OSI model. The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads.
Finally, the higher layers residing above the AAL accept user data, arrange it into packets, and hand it to the AAL. Figure :illustrates the ATM reference model.


Structure of an ATM cell
An ATM cell consists of a 5 byte header and a 48 byte payload. The payload size of 48 bytes was a compromise between the needs of voice telephony and packet networks, obtained by a simple averaging of the US proposal of 64 bytes and European proposal of 32, said by some to be motivated by a European desire not to need echo-cancellers on national trunks.
ATM defines two different cell formats: NNI (Network-network interface) and UNI (User-network interface). Most ATM links use UNI cell format.
Diagram of the UNI ATM Cell
7 4 3 0
GFC VPI
VPI VCI
VCI
VCI PT CLP
HEC




Payload (48 bytes)


Diagram of the NNI ATM Cell
7 4 3 0
VPI
VPI VCI
VCI
VCI PT CLP
HEC




Payload (48 bytes)





GFC = Generic Flow Control (4 bits) (default: 4-zero bits)
VPI = Virtual Path Identifier (8 bits UNI) or (12 bits NNI)
VCI = Virtual channel identifier (16 bits)
PT = Payload Type (3 bits)
CLP = Cell Loss Priority (1-bit)
HEC = Header Error Correction (8-bit CRC, polynomial = X8 + X2 + X + 1)
The PT field is used to designate various special kinds of cells for Operation and Management (OAM) purposes, and to delineate packet boundaries in some AALs.
Several of ATM's link protocols use the HEC field to drive a CRC-Based Framing algorithm, which allows the position of the ATM cells to be found with no overhead required beyond what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and detect multi-bit header errors. When multi-bit header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found.
In a UNI cell the GFC field is reserved for a local flow control/submultiplexing system between users. This was intended to allow several terminals to share a single network connection, in the same way that two ISDN phones can share a single basic rate ISDN connection. All four GFC bits must be zero by default.The NNI cell format is almost identical to the UNI format, except that the 4-bit GFC field is re-allocated to the VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost 212 VPs of up to almost 216 VCs each (in practice some of the VP and VC numbers are reserved).

A Virtual Channel (VC) denotes the transport of ATM cells which have the same unique identifier, called the Virtual Channel Identifier (VCI). This identifier is encoded in the cell header. A virtual channel represents the basic means of communication between two end-points, and is analogous to an X.25 virtual circuit.
A Virtual Path (VP) denotes the transport of ATM cells belonging to virtual channels which share a common identifier, called the Virtual Path Identifier (VPI), which is also encoded in the cell header. A virtual path, in other words, is a grouping of virtual channels which connect the same end-points. This two layer approach results in improved network performance. Once a virtual path is set up, the addition/removal of virtual channels is straightforward





ATM Classes of Services
ATM is connection oriented and allows the user to specify the resources required on a per-connection basis (per SVC) dynamically. There are the five classes of service defined for ATM (as per ATM Forum UNI 4.0 specification). The QoS parameters for these service classes are summarized in Table 1.
Service Class Quality of Service Parameter
constant bit rate (CBR) This class is used for emulating circuit switching. The cell rate is constant with time. CBR applications are quite sensitive to cell-delay variation. Examples of applications that can use CBR are telephone traffic (i.e., nx64 kbps), videoconferencing, and television.
variable bit rate–non-real time (VBR–NRT) This class allows users to send traffic at a rate that varies with time depending on the availability of user information. Statistical multiplexing is provided to make optimum use of network resources. Multimedia e-mail is an example of VBR–NRT.
variable bit rate–real time (VBR–RT) This class is similar to VBR–NRT but is designed for applications that are sensitive to cell-delay variation. Examples for real-time VBR are voice with speech activity detection (SAD) and interactive compressed video.
available bit rate (ABR) This class of ATM services provides rate-based flow control and is aimed at data traffic such as file transfer and e-mail. Although the standard does not require the cell transfer delay and cell-loss ratio to be guaranteed or minimized, it is desirable for switches to minimize delay and loss as much as possible. Depending upon the state of congestion in the network, the source is required to control its rate. The users are allowed to declare a minimum cell rate, which is guaranteed to the connection by the network.
unspecified bit rate (UBR) This class is the catch-all, other class and is widely used today for TCP/IP.

Technical Parameter Definition
cell loss ratio (CLR) CLR is the percentage of cells not delivered at their destination because they were lost in the network due to congestion and buffer overflow.
cell transfer delay (CTD) The delay experienced by a cell between network entry and exit points is called the CTD. It includes propagation delays, queuing delays at various intermediate switches, and service times at queuing points.
cell delay variation (CDV) CDV is a measure of the variance of the cell transfer delay. High variation implies larger buffering for delay-sensitive traffic such as voice and video.
peak cell rate (PCR) The maximum cell rate at which the user will transmit. PCR is the inverse of the minimum cell inter-arrival time.
sustained cell rate (SCR) This is the average rate, as measured over a long interval, in the order of the connection lifetime.
burst tolerance (BT) This parameter determines the maximum burst that can be sent at the peak rate. This is the bucket-size parameter for the enforcement algorithm that is used to control the traffic entering the network.


Benefits of ATM
The benefits of ATM are the following:
• high performance via hardware switching
• dynamic bandwidth for bursty traffic
• class-of-service support for multimedia
• scalability in speed and network size
• common LAN/WAN architecture
• opportunities for simplification via VC architecture
• international standards compliance
ATM Adaptation Layers (AAL)
The use of Asynchronous Transfer Mode (ATM) technology and services creates the need for an adaptation layer in order to support information transfer protocols, which are not based on ATM. This adaptation layer defines how to segment and reassemble higher-layer packets into ATM cells, and how to handle various transmission aspects in the ATM layer.
Examples of services that need adaptations are Gigabit Ethernet, IP, Frame Relay, SONET/SDH, UMTS/Wireless, etc.
The main services provided by AAL (ATM Adaptation Layer) are:
• Segmentation and reassembly
• Handling of transmission errors
• Handling of lost and misinserted cell conditions
• Timing and flow control
The following ATM Adaptation Layer protocols (AALs) have been defined by the ITU-T. It is meant that these AALs will meet a variety of needs. The classification is based on whether a timing relationship must be maintained between source and destination, whether the application requires a constant bit rate, and whether the transfer is connection oriented or connectionless.
• AAL Type 1 supports constant bit rate (CBR), synchronous, connection oriented traffic. Examples include T1 (DS1), E1, and x64 kbit/s emulation.
• AAL Type 2 supports time-dependent Variable Bit Rate (VBR-RT) of connection-oriented, synchronous traffic. Examples include Voice over ATM. AAL2 is also widely used in wireless applications due to the capability of multiplexing voice packets from different users on a single ATM connection.
• AAL Type 3/4 supports VBR, data traffic, connection-oriented, asynchronous traffic (e.g. X.25 data) or connectionless packet data (e.g. SMDS traffic) with an additional 4-byte header in the information payload of the cell. Examples include Frame Relay and X.25.
• AAL Type 5 is similar to AAL 3/4 with a simplified information header scheme. This AAL assumes that the data is sequential from the end user and uses the Payload Type Indicator (PTI) bit to indicate the last cell in a transmission. Examples of services that use AAL 5 are classic IP over ATM, Ethernet Over ATM, SMDS, and LAN Emulation (LANE). AAL 5 is a widely used ATM adaptation layer protocol. This protocol was intended to provide a streamlined transport facility for higher-layer protocols that are connection oriented.
AAL 5 was introduced to:
• reduce protocol processing overhead.
• reduce transmission overhead.
• ensure adaptability to existing transport protocols.
T AAL1 PDU
The structure of the AAL1 PDU is given in the following illustration:
SN
SNP

CSI SC CRC EPC SAR PDU Payload
1 bit 3 bits 3 bits 1 bit 47 bytes
AAL1 PDU
SN
Sequence number. Numbers the stream of SAR PDUs of a CPCS PDU (modulo 16). The sequence number is comprised of the CSI and the SN.
CSI
Convergence sublayer indicator. Used for residual time stamp for clocking.
SC
Sequence count. The sequence number for the entire CS PDU, which is generated by the Convergence Sublayer.
SNP
Sequence number protection. Comprised of the CRC and the EPC.
CRC
Cyclic redundancy check calculated over the SAR header.
EPC
Even parity check calculated over the CRC.
SAR PDU payload
47-byte user information field.
AAL2
AAL2 provides bandwidth-efficient transmission of low-rate, short and variable packets in delay sensitive applications. It supports VBR and CBR. AAL2 also provides for variable payload within cells and across cells. AAL type 2 is subdivided into the Common Part Sublayer (CPS ) and the Service Specific Convergence Sublayer (SSCS ).
AAL2 CPS Packet
The CPS packet consists of a 3 octet header followed by a payload. The structure of the AAL2 CPS packet is shown in the following illustration.
CID LI UUI HEC Information payload
8 bits 6 bits 5 bits 5 bits 1-45/64 bytes
AAL2 CPS packet
CID Channelidentification.
LI
Length indicator. This is the length of the packet payload associated with each individual user. Value is one less than the packet payload and has a default value of 45 bytes (may be set to 64 bytes).
UUI
User-to-user indication. Provides a link between the CPS and an appropriate SSCS that satisfies the higher layer application
HEC
Header error control.
AAL2
The structure of the AAL2 SAR PDU is given in the following illustration.
Start field
CPS-PDU payload

OSF SN P AAL2 PDU payload PAD
6 bits 1 bit 1 bit 0-47 bytes
AAL2 CPS PDU
OSF
Offset field. Identifies the location of the start of the next CPS packet within the CPS-PDU.
SN
Sequence number. Protects data integrity.
P
Parity. Protects the start field from errors.
SAR PDU payload
Information field of the SAR PDU.
PAD
Padding.
AAL2 SSCS Packet
The SSCS conveys narrowband calls consisting of voice, voiceband data or circuit mode data. SSCS packets are transported as CPS packets over AAL2 connections. The CPS packet contains a SSCS payload. There are 3 SSCS packet types.
Type 1 Unprotected; this is used by default.
Type 2 Partially protected.
Type 3 Fully protected: the entire payload is protected by a 10-bit CRC which is computed as for OAM cells. The remaining 2 bits of the 2-octet trailer consist of the message type field.
AAL2 SSCS Type 3 Packets:
The type 3 packets are used for the following:
• Dialled digits
• Channel associated signalling bits
• Facsimile demodulated control data
• Alarms
• User state control operations.
The following illustration gives the general sturcture of AAL2 SSCS Type 3 PDUs. The format varies and each message has its own format according to the actual message type.
Redundancy Time stamp Message dependant information Message type CRC-10
2 14 16 6 10 bits


AAL2 SSCS Type 3 PDU
Redundancy
Packets are sent 3 times to ensure error correction. The value in this field signifies the transmission number.
Time stamp
Counters packet delay variation and allows a receiver to accurately reproduce the relative timing of successive events separated by a short interval.
Message dependant information
Packet content that varies, depending on the message type.
Message type
The message type code.
CRC-10
The 10-bit CRC.
AAL3/4
AAL3/4 consists of message and streaming modes. It provides for point-to-point and point-to-multipoint (ATM layer) connections. The Convergence Sublayer (CS) of the ATM Adaptation Layer (AAL) is divided into two parts: service specific (SSCS ) and common part (CPCS ). This is illustrated in the following diagram:
AAL3/4 packets are used to carry computer data, mainly SMDS traffic.
AAL3/4 CPCS PDU
The functions of the AAL3/4 CPCS include connectionless network layer (Class D), meaning no need for an SSCS; and frame relaying telecommunication service in Class C. The CPCS PDU is composed of the following fields:
Header Info
Trailer

CPI Btag Basize CPCS SDU Pad 0 Etag Length
1 1 2 0-65535 0-3 1 1 2 bytes
AAL3/4 CPCS PDU

CPI
Message type. Set to zero when the BAsize and Length fields are encoded in bytes.
Btag
Beginning tag. This is an identifier for the packet. It is repeated as the Etag.
BAsize
Buffer allocation size. Size (in bytes) that the receiver has to allocate to capture all the data.
CPCS SDU
Variable information field up to 65535 bytes.
PAD
Padding field which is used to achieve 32-bit alignment of the length of the packet.
0
All-zero.
Etag
End tag. Must be the same as Btag.
Length
Must be the same as BASize.
AAL3/4 SAR PDU
The structure of the AAL3/4 SAR PDU is illustrated below:
ST SN MID Information LI CRC
2 4 10 352 6 10 bits




2-byte header 44 bytes 2-byte trailer
48 bytes
AAL3/4 SAR PDU
ST
Segment type. Values may be as follows:
SN
Sequence number. Numbers the stream of SAR PDUs of a CPCS PDU (modulo 16).
MID
Multiplexing identification. This is used for multiplexing several AAL3/4 connections over one ATM link.
Information
This field has a fixed length of 44 bytes and contains parts of CPCS PDU.
LI
Length indication. Contains the length of the SAR SDU in bytes, as follows:
CRC
Cyclic redundancy check.
Functions of AAL3/4 SAR include identification of SAR SDUs; error indication and handling; SAR SDU sequence continuity; multiplexing and demultiplexing.
AAL5 The type 5 adaptation layer is a simplified version of AAL3/4. It also consists of message and streaming modes, with the CS divided into the service specific and common part. AAL5 provides point-to-point and point-to-multipoint (ATM layer) connections.
AAL5 is used to carry computer data such as TCP/IP. It is the most popular AAL and is sometimes referred to as SEAL (simple and easy adaptation layer).
AAL5 CPCS PDU
The AAL5 CPCS PDU is composed of the following fields:
Info
Trailer

CPCS payload Pad UU CPI Length CRC
0-65535 0-47 1 1 2 4 bytes
AAL5 CPCS PDU
CPCS
The actual information that is sent by the user. Note that the information comes before any length indication (as opposed to AAL3/4 where the amount of memory required is known in advance).
Pad
Padding bytes to make the entire packet (including control and CRC) fit into a 48-byte boundary.
UU
CPCS user-to-user indication to transfer one byte of user information.
CPI
Common part indicator is a filling byte (of value 0). This field is to be used in the future for layer management message indication.
Length
Length of the user information without the Pad.
CRC
CRC-32. Used to allow identification of corrupted transmission.
AAL5 SAR PDU The structure of the AAL5 CS PDU is as follows:
Information PAD UU CPI Length CRC-32
1-48 0-47 1 1 2 4 bytes


8-byte trailer
AAL5 SAR PDU
High-Speed LANs
Emergence of High-Speed LANs
 2 Significant trends
– Computing power of PCs continues to grow rapidly
– Network computing
 Examples of requirements
– Centralized server farms
– Power workgroups
– High-speed local backbone
Classical Ethernet
 Bus topology LAN
 10 Mbps
 CSMA/CD medium access control protocol
 2 problems:
– A transmission from any station can be received by all stations
– How to regulate transmission


Solution to First Problem
 Data transmitted in blocks called frames:
– User data
– Frame header containing unique address of destination station

CSMA/CD
Carrier Sense Multiple Access/ Carrier Detection

 If the medium is idle, transmit.
 If the medium is busy, continue to listen until the channel is idle, then transmit immediately.
 If a collision is detected during transmission, immediately cease transmitting.
 After a collision, wait a random amount of time, then attempt to transmit again (repeat from step 1).





Medium Options at 10Mbps

 10Base5
– 10 Mbps
– 50-ohm coaxial cable bus
– Maximum segment length 500 meters
 10Base-T
– Twisted pair, maximum length 100 meters
– Star topology (hub or multipoint repeater at central point)



Hubs and Switches
Hub
 Transmission from a station received by central hub and retransmitted on all outgoing lines
 Only one transmission at a time

Layer 2 Switch
 Incoming frame switched to one outgoing line
 Many transmissions at same time





Bridge
 Frame handling done in software
 Analyze and forward one frame at a time
 Store-and-forward

Layer 2 Switch
 Frame handling done in hardware
 Multiple data paths and can handle multiple frames at a time
 Can do cut-through
Layer 2 Switches
 Flat address space
 Broadcast storm
 Only one path between any 2 devices

 Solution 1: subnetworks connected by routers
 Solution 2: layer 3 switching, packet-forwarding logic in hardware

Benefits of 10 Gbps Ethernet over ATM
 No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells
 Network is Ethernet, end to end
 IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM
 Wide variety of standard optical interfaces for 10 Gbps Ethernet
Fibre Channel
 2 methods of communication with processor:
– I/O channel
– Network communications
 Fibre channel combines both
– Simplicity and speed of channel communications
– Flexibility and interconnectivity of network communications









I/O channel
 Hardware based, high-speed, short distance
 Direct point-to-point or multipoint communications link
 Data type qualifiers for routing payload
 Link-level constructs for individual I/O operations
 Protocol specific specifications to support e.g. SCSI
Fibre Channel Network-Oriented Facilities
 Full multiplexing between multiple destinations
 Peer-to-peer connectivity between any pair of ports
 Internetworking with other connection technologies
Fibre Channel Requirements
 Full duplex links with 2 fibres/link
 100 Mbps – 800 Mbps
 Distances up to 10 km
 Small connectors
 high-capacity
 Greater connectivity than existing multidrop channels
 Broad availability
 Support for multiple cost/performance levels
 Support for multiple existing interface command sets
Fibre Channel Protocol Architecture
 FC-0 Physical Media
 FC-1 Transmission Protocol
 FC-2 Framing Protocol
 FC-3 Common Services
 FC-4 Mapping

Wireless LAN Requirements
 Throughput
 Number of nodes
 Connection to backbone
 Service area
 Battery power consumption
 Transmission robustness and security
 Collocated network operation
 License-free operation
 Handoff/roaming
 Dynamic configuration


IEEE 802.11 Services
 Association
 Reassociation
 Disassociation
 Authentication
 Privacy