CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

MISC Basic Networking Notes
- The most common network user applications on today’s networks are email, web browsers,
instant messaging, collaboration, and databases.
- Below are the 3 categories of network applications:
i) Batch applications are started by a human complete with no other interaction, eg: FTP
and TFTP.
ii) Interactive applications include database updates and queries. A person requests data
from the server and waits for a reply. Response time depends more on the server than the
network.
iii) Real-time applications include VoIP and video. Network bandwidth is critical as these
applications are time critical. Quality of Service (QoS) and sufficient network bandwidth
are mandatory for these applications.
The LLC – Logical Link Control (IEEE 802.2)
- LLC was originated from the High-Level Data Link Control (HDLC) and uses a subset of the
HDLC specification. It is the upper data link sublayer that provides an interface for upper layers
to deal with any type of MAC lower sublayer, eg: 802.3 Ethernet and 802.5 Token Ring in order
to achieve physical media independence. It is used for managing the data link communication,
defining Service Access Points (SAPs) to identify and encapsulate network layer protocols.
Note: LLC is the same for various physical media, eg: Ethernet, Token Ring, and WLAN.
- LLC defines 3 types of operations (or services) for data communication:
LLC Type 1 Connectionless and unreliable. Allows network layer protocols to run on it.
Generally used by network layer protocols that using a transport layer.
LLC Type 2 Connection-oriented and reliable. Allows the LLC sublayer to provide
connection establishment, data acknowledgement, error recovery, and flow
control (windowing or sliding window). A retransmission timer is started when
an endpoint sends frames to its peer. The frames will be retransmitted if an
acknowledgment is not received within the timeout interval.
Generally used in LAN environments where network and transport layer
protocols are not involved.
LLC Type 3 Connectionless and reliable.
- Connection-oriented LLC (LLC2) uses a 2-byte Control field (in the 802.2 LLC header).
Late Collision
- Late collision is a type of collisions found in the CSMA/CD environment where a collision error
is detected after the first 64 bytes of the frame have been sent. It occurs when 2 end systems
encounter a collision upon frame transmission even they have performed collision detection.
This condition can occur when the network is so large that the frame propagation from one end
to another takes longer than the time used to perform collision detection.
- Late collisions are not retransmitted by the NIC (Layer 2). They are left for the upper layers
(eg: TCP) to detect and recover the loss of data.
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com