Direct network links

Modern media

Encoding techniques

Framing

        Need for framing
        Byte oriented
                sentinel approach and escape characters
                byte counting
        Bit oriented
                bit stuffing
        Clock based - SONET

Error detection and correction

        detection
                crc
                parity - simple and two-dimensional
                internet check sum
        correction
                nothing
                forward error correction
                backward

Reliable end-end - in order, correct, at a reasonable pace

        stop-and-wait
        sliding window -
                go back n
                selective repeat
        flow control

Media Access Control

        Ethernet
        FDDI
        not network adaptors

Packet switching

4.1 Switching and Forwarding

Source Routing

        encoding options (list of nodes, list of ports,)
        rotate, delete, pointer
        +optimal
        -source omniscence, length and man of hdr, scaling

Virtual Circuit switching

        operation and relative numbering
        +per packet overhead
        -man of link failure
        - still has routing
        - setup - one RTT
        = using buffers for hop-by-hop flow control

Datagrams

        + no RTT
        - no guaranteed delivery
        +failure of nodes
        -overhead
        congestion versus contention
                congestion control source/dest pairing
                end-end with slow start
                end-end with feedback

Implementation

        the workstation as a switch
                +free
                - coding
                -performance, oss
        on-card switching
4.2  Routing
        distance vector tells your neighbors what you think you know about

the whole world. link state tells what you think is the world what you know about your neighbors

        .2 Distance Vector
                per node exchange with neighbors of routing tables
                (dest, cost, next hop)
                updates - periodic and triggered
                link failure issues and convergence
                        hold down, split horizon, sh with poison reverse
        .3 Link State
                global knowledge and a map of the world at each node
                reliable flooding for dissemination
                        LSP (id, link cost, seqno, ttl)
                        forwarding strategies
                        per node expiration
                route calculation
                        Dijkstra's algorithm - shortest path
                +self-stabilizing, not much traffic, responds to change
                -scalability at each node
        .4 Metrics
                each hop 1
                        - no latency, no speed, no load
                arpanet v1 - hop+queue length
                        - no latency or speed
                arpanet v2 - delay  (delay=depttime-arrivetime+transtime+latency
                        - route flapping
                        - low speed high latency paths totally ignored
                arpanet v3 - compress dynamic range of metric and smooth
variation over time
        .5 Routing, Addressing and Hierarchy
                reachability at borders
4.3  Cell Switching (ATM)
        .1 Cells
                Cell size
                Cell format
        .2 Segmentation and Reassembly
                frequency and load of sar
                ATM Adaption layer 3/4
                        intermediate cs-pdu  - has added header and trailer
to encapsulate, inform far atm switch, etc.
                        then 44 byte units of csu-pdu get placed in cells,
with the 4 byte of remaining payload header and trailer for each cell.
                ATM adaptation layer 5
                        trades aal layer for access to one bit in atm hdr
        .3 Virtual Paths
                8bit VPI and 16bit VCI
                VPI for external routing, VCI for internal and full
                LAN emulation
                        broadcast and multicast use
                        redo protocols such as ARP, find file server in
Novell, etc
                        alternatively, emulate multicast and broadast in switch